The human brain is the central organ of the human nervous system, and with the spinal cord makes the central nervous system. The brain consists of cerebrum, brain stem and cerebellum. It controls most of the body's activities, processes, integrates, and coordinates the information it receives from the sense organs, and makes decisions about instructions sent throughout the body. The brain is contained in, and protected by, the skull's skull. The cerebrum is the largest part of the human brain. It is divided into two hemispheres. The cerebral cortex is the outer layer of gray matter, which encompasses the core of white matter. The cortex is divided into neocortex and a much smaller allocation. The neocortex consists of six neuronal layers, while allocortex has three or four. Each hemisphere is conventionally divided into four frontal, temporal, parietal, and occipital lobes. The frontal lobes are associated with executive functions including self-control, planning, reasoning, and abstract thinking, while the occipital lobe is dedicated to vision. In each lobe, cortical areas are associated with specific functions, such as sensory, motor and association areas. Although the left and right hemispheres have almost identical forms and functions, some functions are associated with one side, such as the language on the left and the visual-spatial ability on the right. The hemisphere is connected by the comic nerve ducts, the largest being the corpus callosum.
The cerebrum is connected by the brain stem to the spinal cord. The brain stem consists of the midbrain, the pons, and the medulla oblongata. The cerebellum is connected to the brainstem by a channel pair. In the cerebrum is a ventricular system, consisting of four interconnected ventricles in which cerebrospinal fluid is produced and circulated. Below the cerebral cortex are some important structures, including the thalamus, epithalamus, pineal gland, hypothalamus, pituitary gland, and subthalamus; limbic structures, including the amygdala and the hippocampus; claustrum, various core basal ganglia; basal brain structure, and three circumventricular organs. The brain cells include neurons and supportive glial cells. There are more than 86 billion neurons in the brain, and the number of other cells is more or less the same. Brain activity is made possible by the interconnection of neurons and the release of their neurotransmitters in response to nerve impulses. Neurons are connected to form neural pathways, neural circuits, and complex network systems. The whole circuit is driven by a neurotransmission process.
The brain is protected by the skull, suspended in cerebrospinal fluid, and isolated from the bloodstream by the blood-brain barrier. However, the brain is still vulnerable to damage, disease, and infection. Damage can be caused by trauma, or loss of blood supply known as stroke. The brain is prone to degenerative disorders, such as Parkinson's disease, dementia including Alzheimer's disease, and multiple sclerosis. Psychological conditions, including schizophrenia and clinical depression, are thought to be related to brain dysfunction. The brain can also be a tumor, both benign and malignant; This mostly comes from other sites in the body. The study of brain anatomy is neuroanatomy, while the study of its function is neuroscience. A number of techniques are used to study the brain. Specimens from other animals, which can be microscopically examined, have traditionally provided much information. Medical imaging technologies such as functional neuroimaging imaging, and electroencephalography (EEG) are important in brain study. The medical history of people with brain injuries has provided insight into the functioning of every part of the brain.
In culture, the philosophy of mind over the centuries seeks to answer the question of the nature of consciousness and the mind-body problem. The pseudoscience of phrenology attempted to localize the attributes of personality to the cortical regions of the 19th century. In science fiction, brain transplants are envisioned in fairy tales like 1942 Donovan's Brain .
Video Human brain
Structure
Gross anatomy
The adult human brain weighs on average about 1.2-1.4 kg (2.6-3.1 pounds) which is about 2% of the total body weight, with a volume of about 1260 cm 3 at men and 1130 cm 3 in women, although there are substantial individual variations. Neurological differences between the sexes have not been shown to correlate in any simple way with IQ or other measures of cognitive performance.
The cerebrum, which consists of the cerebral hemispheres, forms the largest part of the brain and lies above other brain structures. The outer region of the cerebral hemisphere, the cerebral cortex, is a gray matter, consisting of a cortical layer of neurons. Each hemisphere is divided into four main lobes.
Brain stem, resembling stalks, sticking and leaving cerebrum at the beginning of the central brain area. Brain stubs include central brains, pons, and medulla oblongata. Behind the brainstem is cerebellum (Latin: small brain ).
Cerebrum, brain stem, cerebellum, and spinal cord are covered by three membranes called meninges. Membranes are a difficult dura mater; the middle arachnoid material and the smoother pia mater. Between the arachnoid mater and the pia mater is the subarachnoid space, which contains cerebrospinal fluid. In the cerebral cortex, close to the basal membrane of the pia mater, is a boundary membrane called glia limitans; this is the outermost membrane of the cortex. The brain that lives very gently, has a gel-like consistency similar to soft tofu. The cortical layers of the neurons make up most of the gray matter of the brain, while the deeper subcortical regions of the myelin axons, forming white matter.
Cerebrum
The cerebrum is the largest part of the human brain, and is divided into almost right and left hemisphere symmetries by deep grooves, longitudinal fissures. The outer part of the cerebrum is the cerebral cortex, composed of gray matter arranged in layers. Its height is 2-4 millimeters (0.079 to 0.157 inches), and is very folded to produce a convoluted look. Below the cortex is the white matter of the brain. The largest part of the cerebral cortex is the neocortex, which has six neuronal layers. The rest of the cortex is allocortex, which has three or four layers. The hemisphere is connected by five commissures that span longitudinal fissures, the largest of these being the corpus callosum. The surface of the brain is folded into the mountains (gyri) and grooves (sulci), many of which are named, usually by position, such as frontal lobe or frontal lobe gyrus that separates the central regions of the cerebral hemispheres.. There are many minor variations in the secondary and tertiary folds. Each hemisphere is conventionally divided into four lobes; the frontal lobes, the parietal lobes, the temporal lobes, and the occipital lobes, are named after the skull bone through which it passes. Each lobe is associated with one or two special functions although there is some functional overlap between them.
The cortex is mapped by the division into about fifty different functional areas known as the Brodmann area. These areas are distinctly different when viewed under a microscope. The cortex is divided into two main functional areas - the motor cortex and the sensory cortex. The primary motor cortex, which sends axons to motor neurons in the brainstem and spinal cord, occupies the back of the frontal lobe, just in front of the somatosensory area. The main sensory areas receive signals from the sensory nerves and tracts by means of nuclear relays in the thalamus. Primary sensory areas include the visual cortex of the occipital lobe, the auditory cortex in the temporal lobe and the insular cortex, and the somatosensory cortex in the parietal lobe. The remaining parts of the cortex, called the association area. These areas receive input from the sensory area and the lower part of the brain and engage in complex cognitive processes of perception, thought, and decision making. The main function of the frontal lobe is to control attention, abstract thinking, behavior, problem-solving tasks, and physical and personality reactions. The occipital lobe is the smallest lobe; Its main functions are visual reception, visual-spatial processing, movement, and color recognition. There is a smaller occipital lobe in the lobe known as cuneus. The temporal lobes control the auditory and visual memory, language, and some hearing and speech.
Serebrum contains a ventricle in which cerebrospinal fluid is produced and circulated. Below the corpus callosum is the pellucidum septum, the membrane separating the lateral ventricle. Below the lateral ventricles is the thalamus and forwards and below is the hypothalamus. The hypothalamus leads to the pituitary gland. Behind the thalamus is the brainstem.
Basal ganglia, also called basal nuclei, are a set of distant structures within the hemispheres involved in movement behavior and regulation. The largest component is the striatum, the other is globus pallidus, substansia nigra and subthalamic nuclei. Part of the dorsal striatum, putamen, and globus pallidus, is located separately from the lateral and thalamus ventricles by the internal capsule, whereas the caudate nucleus stretches around and borders the lateral ventricle on its outer side. At the deepest part of the lateral sulcus between the insular cortex and the striatum is a thin neuronal sheet called claustrum. Some sources include these with basal ganglia.
Below and in front of the striatum there are a number of basal front brain structures. These include nucleus accumbens, basal nucleus, Broca's diagonal band, substantia innominata, and medial septal nuclei. This structure is important in producing neurotransmitters, acetylcholine, which are then widely distributed throughout the brain. The basal brain, especially the core basalis, is considered the main cholinergic output of the central nervous system to the striatum and neocortex.
Cerebellum
The cerebellum is divided into the anterior lobe, the posterior lobe, and the flocculonodular lobe. The anterior and posterior lobes are connected in the middle by the vermis. The small brain has a much thinner outer cortex that shrinks horizontally. Seen from the bottom between the two lobes is the third lobe of the flocculonodular lobe. The small brain lies behind the cranial cavity, lying beneath the occipital lobe, and separated from it by the cerebellar tentorium, a piece of fiber.
It is connected to the midbrain of the brain stem by the superior cerebellar stem, to the pons by the central cerebellum gag, and to the medulla by the inferior peduncle peduncellar. The small brain consists of the inner medulla of white matter and the outer cortex of the richly folded gray matter. The anterior and posterior lobes of the cerebellum appear to play a role in coordinating and refining complex motor movements, and the flocculonodular lobes in the maintenance of balance even though the debate exists for cognitive, behavioral and motor functions.
Brainstem
Brain stem is located below cerebrum and consists of central brains, pons and medulla. It is located on the back of the skull, resting on the base known as clivus, and ends on foramen magnum, a large opening in the occipital bone. Brain rods continue below as a spinal cord, protected by the vertebral column.
Ten of the twelve pairs of cranial nerves arise directly from the brainstem. The brain stem also contains many nuclei of the cranial nerves and peripheral nerve nuclei, as well as the nuclei involved in the regulation of many important processes including breathing, eye movement control and balance. The formation of reticular, ill defined formation nucleic tissue, present in and along the brain stem. Many neural channels, which transmit information to and from the cerebral cortex throughout the body, pass through the brainstem.
Microanatomy
The human brain consists mainly of neurons, glial cells, neural stem cells, and blood vessels. Types of neurons include interneurons, pyramidal cells including Betz cells, motor neurons (upper and lower motor neurons), and Purkinje cerebellar cells. The Betz cells are the largest cells (based on body cell size) in the nervous system. The adult human brain is thought to contain 86 Â ± 8 billion neurons, with approximately the same number (85 Â ± 10 billion) non-neuronal cells. Of these neurons, 16 billion (19%) are located in the cerebral cortex, and 69 billion (80%) are in the cerebellum.
The types of glial cells are astrocytes (including Bergmann glia), oligodendrocytes, ependymal cells (including tanycytes), radial glial cells and microglia. Astrocytes are the largest glial cells. They are stellate cells with many processes radiating from their cell bodies. Some of these processes end up as perivascular end-feet in capillary walls. The glia boundary of the cortex consists of an astrocytic foot process that partially contains brain cells.
Mast cells are white blood cells that interact in the neuroimmune system in the brain. Mast cells in the central nervous system are present in a number of brain structures and in the meninges; they mediate the neuroimmun response in inflammatory conditions and help maintain blood-brain barrier, especially in regions of the brain where barriers do not exist. Across the system, mast cells act as the primary effector cells in which pathogens can affect the intestinal axis-the brain.
About 400 genes proved to be brain specific. In all ELAVL3 neurons expressed, and in pyramidal neurons NRGN and REEP2 are also expressed. GAD1 is important for the biosynthesis of GABA neurotransmitters expressed in interneurons. Proteins expressed in glial cells are GFAP astrocyte markers, and S100B. The basic myelin protein and the OLIG2 transcription factor are expressed in oligodendrocytes.
Cerebrospinal fluid
Cerebrospinal fluid is a clear and colorless transelular fluid that circulates around the brain in the subarachnoid space, in the ventricular system, and in the spinal cord central canal. It also fills some gaps in the subarachnoid space, known as subarachnoid cisterns. Four ventricle, two lateral, one-third, and fourth ventricle, all containing choroid plexus which produce cerebrospinal fluid. The third ventricle is located in the midline and connected to the lateral ventricle. A single channel, the cerebral aqueduct between the pons and the cerebellum, connects the third ventricle to the fourth ventricle. Three separate openings, the middle and two lateral holes, drain the cerebrospinal fluid from the fourth ventricle to the cisterna magna of one of the main tanks. From this, cerebrospinal fluid circulates around the brain and spinal cord in the subarachnoid space, between the arachnoid mater and the pia mater. At one time, there were about 150mL of cerebrospinal fluid - mostly in subarachnoid space. It is constantly regenerated and absorbed, and replaces about once every 5-6 hours.
In other parts of the body, the circulation in the lymphatic system cleans the extracellular waste products from the cell tissues. For brain tissue, such systems have not been identified. However, the presence of glymphatic or paravascular systems has been proposed. A newer study (2015) from two laboratories shows the presence of lymphatic meningeal vessels that run along the veins, and this has been shown with lymph valves, becoming wider at the base of the brain where they come out with cranial nerves.
Blood supply
The internal carotid artery supplies oxygenated blood to the front of the brain and the vertebral artery supplies blood to the back of the brain. These two circulations join together in the circle of Willis, a circular artery connected located in the interpeduncular channel between the midbrain and the pons.
The internal carotid artery is a branch of the common carotid artery. They enter the cranium through the carotid canal, traveling through the cavernous sinus and entering the subarachnoid space. They then enter the Willis circle, with two branches, the anterior cerebral artery appears. These branches move forward and then upward along longitudinal slits, and supply the front and midline of the brain. One or more small anterior communicating arteries join the two anterior cerebral arteries as soon as they appear as branches. The internal carotid artery continues forward as the central cerebral artery. They travel sideways along the sphenoid bone from the eye socket, then up through the insula cortex, where the last branches appear. The middle cerebral artery sends a branch along its length.
The vertebral artery appears as a branch of the left and right subclavian arteries. They travel upward through the transverse foramen - space in the cervical vertebra and then appear as two vessels, one on the left and one to the right of the medulla. They remove one of the three branches of the cerebellum. The vertebral artery joins in the middle of the medulla to form a larger basilar artery, which sends several branches to supply the medulla and the pons, and two other anterior and superior cerebellum branches. Finally, the basilar artery is divided into two posterior cerebral arteries. This journey comes out, around the superior cerebellar handle, and along the upper part of the cerebellum tentorium, where it sends a branch to supply the temporal and occipital lobes. Each posterior cerebral artery sends a small posterior communicative artery to join the internal carotid artery.
Blood drainage
Cerebral veins drain deoxygenated blood from the brain. The brain has two main tissue veins: the outer or shallow tissue, on the surface of the three-pronged cerebrum, and the interior tissue. Both of these networks communicate through anastomosing (join) veins. The blood vessels of the brain flow into the larger cavity of the dural vein sinus usually located between the dura mater and the skull cap. The blood from the cerebellum and brain is flowing into the large cerebral vein. Blood from the medulla and brainstem pons have varying drainage patterns, either to the spinal veins or to adjacent cerebral veins.
Blood on the inside of the brain flows, through the venous plexus to the cavernous sinus in front, and the superior and inferior petrosus sinus on the side, and the inferior sagittal sinus at the back. Blood flows from the outer brain to the superior saggital sinus, located in the midline above the brain. The blood from here joins the blood from the sinuses straight at the sinuses.
Blood from here flows into the left and right sinuses that transverse. This then flows into the sigmoid sinus, which receives blood from the cavernous sinuses and the superior and inferior petrosus sinuses. Sigmoid flows into a large internal jugular vein.
The blood-brain barrier
Larger arteries throughout the brain supply blood to smaller capillaries. The smallest blood vessel in the brain, it is lined with cells that are connected with tight intersections and the liquid does not leak inward or leak to the same level as it does in other capillaries, thus creating a blood-brain barrier. Pericytes play a major role in the formation of tight intersections. These barriers are less permeable to larger molecules, but are still permeable to water, carbon dioxide, oxygen, and most fat-soluble substances (including anesthetics and alcohols). Blood-brain barriers do not exist in areas of the brain that may need to respond to fluid changes in the body, such as the pineal gland, the postrema area, and some areas of the hypothalamus. There is a similar cerebrospinal blood-borne barrier, which serves the same purpose as a blood-brain barrier, but facilitates the transport of different substances to the brain due to different structural characteristics between the two barrier systems.
Maps Human brain
Development
At the beginning of the third week of development, the embryo ectoderm forms a thickened strip called a nerve plate. In the fourth week of development, the neural plate has been widened to provide a broad cephalic tip, a wider central portion and a narrow caudal tip. This swelling represents the beginning of the forebrain, the midbrain and the back of the brain. Neural christ cells (derived from the ectoderm) fill the lateral edges of the plates in neural folds. In the fourth week of the neurulation stage the nerve plate folds and closes to form a neural tube, uniting neural crucial cells in a neural emblem. The neural peak runs the length of the tube with neural cranial crystal cells at the cephalic end and the neural tail cells on the tail. The cells escape from the peaks and migrate in craniocaudal waves (head to tail) inside the tube. Cells at the cephalic end cause the brain, and the cells on the caudal end give rise to the spinal cord.
The tube bends as it grows, forming a crescent-shaped moon in the head. The first hemisphere appears on the 32nd day. At the beginning of the fourth week the cephalic part bends forward in a cephalic arch. This folded part becomes the forebrain (prosencephalon); the adjacent part of the arch becomes the midbrain (mesencephalon) and the tail to bending into the back of the brain (rhombencephalon). These three areas are formed as swelling known as primitive vesicles. In the fifth week the development of five brain vesicles has been formed. The forebrain separates into two vesicles an anterior telencephalon and a posterior diencephalon. Telencephalon gives rise to the cerebral cortex, basal ganglia, and related structures. Diencephalon gives rise to the thalamus and hypothalamus. The back brain is also divided into two areas - metencephalon and mylencephalon. Metencephalon causes cerebellum and pons. Myelencephalon gives rise to medulla oblongata. Also during the fifth week, the brain is divided into repeating segments called neuromeres. This is known as a rhombomer seen in the back of the brain.
The characteristics of the brain are gyrification (cortical wrinkling). Inside the womb, the cortex begins smoothly but begins to form a gap that begins to mark different brain lobes. Scientists do not have a clear answer as to why the cortex then wrinkles and creases, but wrinkles and folds are associated with intelligence and nerve disorders. The fissures are formed as a result of an increasing hemisphere that increases in size due to sudden growth in gray matter cells. The underlying white problem did not grow at the same rate and the hemisphere crammed into the small skull lane. The first gap that appears in the fourth month is the lateral cerebral fossa. The end of the expanded tail of the hemisphere should be curved forward to adjust to the limited space. It covers the fossa and converts it into a much deeper back known as the lateral sulcus and this marks the temporal lobe. In the sixth month another sulci has formed which demarcizes the frontal, parietal, and occipital lobes. Genes present in the human genome (ArhGAP11B) may play a major role in gyrification and encephalaliation.
Function
Motor control
The brain's motor system is responsible for the generation and control of movement. The resulting movement moves from the brain through the nerves to the motor neurons in the body, which control muscle work. The corticospinal tract carries movement from the brain, through the spinal cord, to the body and limbs. The cranial nerves carry movements related to the eyes, mouth, and face.
Rough movements - such as movement and movement of the arms and legs - are produced in the motor cortex, divided into three parts: the main motor cortex, found in the prefrontal gyrus and having a section dedicated to the movement of different parts of the body. These movements are supported and governed by two other areas, located anteriorly to the main motor cortex: premotor areas and additional motor areas. Hands and mouths have a much larger area dedicated to them than other body parts, allowing smoother movements; this has been visualized in a motor cortical homunculus. The impulse generated from the motor cortex travels along the corticospinal tract along the front of the medulla and passes (decussate) in the medullary pyramid. It then runs along the spinal cord, with most of it connected to the interneuron, in turn connecting to the lower motor neurons in the gray matter which then sends the impulse to move into the muscle itself. Cerebellum and basal ganglia, play a role in smooth, complex and coordinated muscle movement. The connection between the cortex and the basal ganglia controls muscle tone, posture and movement initiation, and is called the extrapyramidal system.
Sensoric
The sensory nervous system is involved with the reception and processing of sensory information. This information is received through the cranial nerve, through the channel in the spinal cord, and directly in the center of the brain that is exposed to blood. The brain also accepts and interprets information from the particular senses (sight, smell, hearing, and tasting). Motor and sensory signals are also integrated.
From the skin, the brain receives information about subtle touch, pressure, pain, vibration, and temperature. From the joint, the brain receives information about the position of the joint. The sensory cortex is found near the motor cortex, and, like the motor cortex, has an area related to sensations from different parts of the body. The sensation collected by the sensory receptors on the skin is converted into a neural signal, which passes through a series of neurons through a duct in the spinal cord. The medial-dorsal dorsal lemniscine path contains information about the delicate touch, vibration and joint position. Neurons travel to the back of the spinal cord to the back of the medulla, where they connect with a "second order" neuron that immediately exchanges sides. These neurons then walk upwards into the ventrobasal complex in the thalamus where they are connected with a "third order" neuron, and runs into the sensory cortex. The spinotalamic tract carries information about pain, temperature, and rough touch. Neurons travel to the spinal cord and connect with second-order neurons in brainstem reticular formation for pain and temperature, as well as in the medial ventrobasal complex for abrupt touch.
Vision is produced by the light that affects the retina of the eye. Photoreceptors in the retina transduct the sensory stimuli of light into electrical nerve signals sent to the visual cortex in the occipital lobe. Visions from the left visual field are received on the right side of each retina (and vice versa) and pass through the optic nerve until some information changes side, so that all information about one side of the visual plane passes the tract on the opposite side of the brain. The nerve reaches the brain at the lateral geniculate nucleus, and travels through optical radiation to reach the visual cortex.
Hearing and balance are both produced in the inner ear. The movement of fluid in the inner ear is produced by movement (for balance) and transmitted vibrations generated by ossicles (for sound). It creates a nerve signal that passes through the vestibulocochlear nerve. From here, it passes to the core of the cochlea, the superior olivary nucleus, the geniculate medial nucleus, and finally the auditory radiation to the auditory cortex.
The sense of smell is generated by receptor cells in the olfactory mucosal epithelium in the nasal cavity. This information passes through a relatively permeable part of the skull to the olfactory nerve. These nerves transmit to the neural circuit of the olfactory bulb from which information is passed to the olfactory cortex. The flavor is generated from the receptor on the tongue and passes the facial nerve and glossopharyn to the solitary channel in the brainstem. Some flavor information is also passed from the pharynx to this area via the vagus nerve. The information is then passed from here through the thalamus to the hot enhancer cortex.
Rule
The brain's autonomic function includes regulation, or rhythmic control of the heart rate and respiratory rate, and maintains homeostasis.
Blood pressure and heart rate are affected by the vasomotor center of the medulla, which causes the arteries and veins to become confined at rest. This affects the sympathetic and parasympathetic nervous system through the vagus nerve. Information about blood pressure is produced by the baroreceptors in the aortic body in the arch of the aorta, and is passed on to the brain along the afferents of the vagus nerve. Information about pressure changes in the carotid sinus originates from the carotid body located near the carotid artery and is passed through a nerve that joins the glossopharyngeal nerve. This information moves to solitary nuclei in the medulla. Signals from here affect the vasomotor center to adjust the constriction of blood vessels and arteries.
The brain controls the rate of breathing, especially by the respiratory center in the medulla and the pons. The respiratory center controls respiration, by producing a motor signal that is lowered to the spinal cord, along the phrenic nerve to the diaphragm and other respiratory muscles. It is a mixed nerve that carries sensory information back to the center. There are four respiratory centers, three with clearer functions, and apneustic centers with less obvious functions. In the medulla, the dorsal respiratory group causes the desire to breathe and receive sensory information directly from the body. Also in the medulla, the ventral respiratory group affects the exhalation during exertion. In the central pons of the pneumothorax affect the duration of each breath, and the apneustic center appears to have an effect on the inhalation. The respiratory center directly senses carbon dioxide and blood pH. Information on blood oxygen levels, carbon dioxide and pH is also felt in artery walls in peripheral chemoreceptors of the aortic and carotid bodies. This information is passed through the vagus and glossopharyngeal nerves to the respiratory centers. High carbon dioxide, acidic pH, or low oxygen stimulate the respiratory center. The desire to breathe is also affected by pulmonary stretch receptors in the lungs which, when activated, prevent the lungs from overinflating by sending information to the respiratory center through the vagus nerve.
The hypothalamus in the diencephalon, involved in regulating many bodily functions. Functions include neuroendocrine regulation, circadian rhythm setting, autonomic nervous system control, and fluid regulation, and food intake. Circadian rhythms are controlled by two major cell groups in the hypothalamus. The anterior hypothalamus includes the suprachiasmatic nucleus and the ventrolateral preoptic nucleus through the gene expression cycle, resulting in approximately 24 hours of circadian clock. On the day circadian ultradian rhythm controls sleep patterns. Sleep is an essential requirement for the body and brain and allows closure and rest of the body system. There are also findings that show that daily toxin deposition in the brain is removed during sleep. When awake the brain consumes one-fifth of the total energy needs of the body. Sleep always reduces this usage and gives time for energy-boosting ATP recovery. The effects of lack of sleep indicate an absolute necessity for sleep.
The lateral hypothalamus contains orexinergic neurons that control appetite and passion through their projection to the reticular activation system. The hypothalamus controls the pituitary gland by releasing peptides such as oxytocin, and vasopressin, and dopamine into the median eminence. Through autonomous projection, the hypothalamus is involved in regulating functions such as blood pressure, heart rate, breathing, sweating, and other homeostatic mechanisms. The hypothalamus also plays a role in thermal regulation, and when stimulated by the immune system, is capable of producing fever. The hypothalamus is affected by the kidneys - when the blood pressure goes down, the renin released by the kidneys stimulates the need to drink. The hypothalamus also regulates food intake through autonomic signals, and the release of hormones by the digestive system.
Language
While language functions have traditionally been considered to be localized in the Wernicke and Broca areas, it is now largely accepted that wider cortical area networks contribute to language functions.
The study of how language is represented, processed, and obtained by the brain is called neurolinguistics, which is a large multidisciplinary image field of cognitive neuroscience, cognitive linguistics, and psycholinguistics.
Lateralisation
Serebrum has a contralateral organization with each hemisphere interacting primarily with one half of the body: the left side of the brain interacts with the right side of the body, and vice versa. The cause of this development is uncertain. The motor connections from the brain to the spinal cord, and the sensory connections from the spinal cord to the brain, are both intersecting in the brainstem. Visual input follows a more complex rule: the optic nerves of the two eyes join at a point called optical chiasm, and half of the fibers of each nerve separate to join the other. The result is a connection from the left side of the retina, in both eyes, to the left side of the brain, whereas the connection from the right part of the retina leads to the right side of the brain. Since each half of the retina receives light coming from half the visual field, its functional consequence is the visual input from the left side of the world to the right side of the brain, and vice versa. Thus, the right side of the brain receives somatosensory input from the left side of the body, and visual input from the left side of the visual field.
The left and right sides of the brain appear symmetrical, but function asymmetrically. For example, the partner of the left-brain motor area that controls the right hand is the right hemisphere that controls the left hand. However there are some notable exceptions, involving spatial language and cognition. The left frontal lobes are dominant for the language. If the key language area of ​​the left hemisphere is damaged, it can make the victim unable to speak or understand, while equivalent damage to the right hemisphere will only cause minor damage to language skills.
An important part of the current understanding of the interaction between the two hemispheres has come from the study of "brain-split patients" - people who underwent surgical dissection of the corpus callosum in an attempt to reduce the severity of epileptic seizures. These patients do not exhibit unusual behavior that is immediately apparent, but in some cases can behave almost like two different people in the same body, with the right hand taking action and then the left hand removing it. These patients, while briefly showing the image on the right side of the visual fixation point, are able to describe it verbally, but when the image is shown on the left, it can not describe it, but may be able to give an indication with the left hand of the nature of the object shown.
Emotion
Emotion is generally defined as a two-step multicomponent process involving elicitation, followed by psychological feelings, judgments, expressions, autonomous responses, and action trends. The attempt to localize the basic emotions to certain areas of the brain has been controversial, with some research finding no evidence for emotionally appropriate locations, and instead of circuits involved in general emotional processes. The amygdala, orbitofrontal cortex, mid and anterior cortical and lateral incortal cortex prefrontal, appear to be involved in generating emotions, while weak evidence is found for the ventral tegmental area, ventral pallidum and nucleus accumbens in the essentials of incentives. Others, however, have found evidence of activation of certain areas, such as the basal ganglia in happiness, the subcallosal singular cortex in sadness, and the amygdala in fear.
Cognition
The brain is responsible for cognition. The brain gives rise to countless cognitive processes that constitute cognition as a whole; However, higher cognitive functioning comes from a set of executive functions, which is a cognitive process group that allows cognitive control behavior: selecting and successfully monitoring behaviors that facilitate the achievement of the selected objectives. Executive functions include the ability to filter information and eliminate irrelevant stimuli with attention control and cognitive impediments, the ability to process and manipulate information stored in working memory, the ability to think concepts simultaneously and switch tasks with cognitive flexibility, the ability to inhibit impulses and strong responses with inhibitory control, and the ability to determine the relevance of information or the feasibility of an action. The high-level executive function requires the simultaneous use of some basic executive functions and includes fluid planning and intelligence (ie, reasoning and problem solving).
The prefrontal cortex plays an important role in mediating executive function. Neuroimaging during neuropsychological tests of executive function, such as the stroop test and the working memory test, have found that the maturation of the prefrontal cortical cortex correlates with executive function in children. Planning involves the activation of the dorsolateral prefrontal cortex (DLPFC), the anterior cingulate cortex, the angular prefrontal cortex, the right prefrontal cortex, and the supramarginal gyrus. Memory manipulation work involves DLPFC, inferior frontal gyrus, and parietal cortex area. The inhibitory control involves several areas of the prefrontal cortex as well as the caudate nucleus and the subthalamic nucleus. Task shifting does not involve specific parts of the brain, but involves several areas of the prefrontal cortex and the parietal lobe.
Physiology
Neurotransmission
Brain activity is made possible by the interconnection of connected neurons to achieve their targets. Neurons consist of cell bodies, axons, and dendrites. Dendrites are often an extensive branch that receives information in the form of signals from the axon terminal of other neurons. Accepted signals can cause neurons to initiate action potentials (electrochemical signals or nerve impulses) that are shipped with an axon to the axon terminal, to connect with dendrites or with body cells from other neurons. The action potential starts in the initial segment of the axon, which contains the protein complex. When the action potential, reaching the axon terminal it triggers the release of a neurotransmitter in the synapse that propagates a signal acting on the target cell. These chemical neurotransmitters include dopamine, serotonin, GABA, glutamate, and acetylcholine. GABA is a major inhibitory neurotransmitter in the brain, and glutamate is a major excitatory neurotransmitter. Neurons connect to synapses to form neural pathways, neural circuits, and complex large network systems such as meaning networks and default mode networks, and activity between them is driven by neurotransmission processes.
Metabolism
The brain spends up to 20% of the energy used by the human body, more than any other organ. In humans, blood glucose is the main source of energy for most cells and is essential for normal functioning in a number of tissues, including the brain. The human brain consumes about 60% of the blood glucose in individuals who are fasting and immobile. Brain metabolism usually depends on blood glucose as a source of energy, but during low glucose (such as fasting, endurance exercise, or limited carbohydrate intake), the brain uses ketone bodies for fuel with a smaller need for glucose. The brain can also take advantage of lactate while exercising. The brain stores glucose in the form of glycogen, although in a much smaller amount than that found in the liver or skeletal muscle. Long-chain fatty acids can not cross the blood-brain barrier, but the liver can break it down to produce a ketone body. However, short chain fatty acids (eg, butyric acid, propionic acid, and acetic acid) and medium chain fatty acids, octanoic acid and heptanoic acid, can cross the blood brain barrier and are metabolized by brain cells.
Although the human brain represents only 2% of body weight, it receives 15% of cardiac output, 20% of total body oxygen consumption, and 25% of total body glucose utilization. Most brains use glucose for energy, and glucose deprivation, as can occur in hypoglycemia, can lead to loss of consciousness. Brain energy consumption does not vary over time, but the active region of the cortex consumes more energy than the inactive regions: this fact forms the basis for PET and fMRI functional brain imaging methods. This functional imaging technique provides a three-dimensional image of metabolic activity.
Sleep function is not fully understood; However, there is evidence that sleep increases the clearance of metabolic waste products, some of which are potentially neurotoxic, from the brain and also allow repair. Evidence suggests that increased cleaning of metabolic wastes during sleep occurs through enhanced glymphatic system function. Sleep may also affect cognitive function by weakening unnecessary connections.
Research
The brain is not fully understood, and research is ongoing. Neurologists, along with researchers from various disciplines, study how the human brain works. The boundary between neuroscience specialization, neurology and other disciplines such as psychiatry has faded as they are all influenced by basic research in neuroscience.
Neuroscience research has grown tremendously in recent decades. The "Decade of the Brain", an initiative of the United States Government in the 1990s, is thought to have marked much improvement in research, and followed in 2013 by the BRAIN Initiative. The Human Connectome Project is a five-year study launched in 2009 to analyze the anatomical and functional connections of parts of the brain, and has provided a wealth of data.
Method
Information about the structure and function of the human brain comes from a variety of experimental methods, including animals and humans. Information about brain trauma and stroke has provided information about the functioning of the brain and the effects of brain damage. Neuroimaging is used to visualize the brain and record brain activity. Electrophysiology is used to measure, record and monitor the electrical activity of the cortex. Measurements can be local terrain potentials from the cortical area, or the activity of a single neuron. The electroencephalogram can record the electrical activity of the cortex using electrodes placed non-invasively on the scalp.
Invasive measures include electrocorticography, which uses electrodes placed directly on open surfaces of the brain. This method is used in mapping cortical stimulation, used in the study of the relationship between the cortical area and their systemic function. By using much smaller microelectrodes, single-unit recordings can be made from one neuron that provides high spatial resolution and high temporal resolution. It has enabled connecting brain activity with behavior, and the creation of neuronal maps.
Imaging
Functional neuroimaging techniques show changes in brain activity associated with certain brain area functions. One technique is functional magnetic resonance imaging (fMRI) that has advantages over previous SPECT and PET methods that do not require the use of radioactive materials and offer higher resolution. Another technique is near-infrared functional spectroscopy. This method relies on hemodynamic responses that show changes in brain activity in relation to changes in blood flow, useful in mapping functions to the area of ​​the brain. Rest fMRI countries see the interaction of brain regions while the brain does not perform certain tasks. This is also used to indicate default mode network.
Every electric current generates a magnetic field; nerve oscillations induce a weak magnetic field, and in functional magnetoencephalography the resulting current may show localized brain function in high resolution. Tractography uses MRI and image analysis to create 3D images of the brain's nerve ducts. The Connectogram provides a graphical representation of the brain's neural connections.
The differences in brain structure can be measured in some disorders, especially schizophrenia and dementia. Different biological approaches using imagery have given more insights for example into depressive disorder and obsessive-compulsive disorder. The main source of information about the functioning of the brain region is the effect of damage on them.
Advances in neuroimaging have enabled objective insight into mental disorders, leading to faster diagnosis, more accurate prognosis, and better monitoring.
Gene and protein expression
Bioinformatics is a field of study that includes the creation and development of databases, and computational and statistical techniques, which can be used in the study of the human brain, particularly in the field of genes and protein expression. Bioinformatics and studies in genomics, and functional genomics, result in the need for DNA annotations, transcripttome technology, identify genes, and their location and function. GeneCards is the main database.
By 2017, just under 20,000 protein-encoding genes are seen expressed in humans, and about 400 of these genes are brain-specific. The data already provided on gene expression in the brain has sparked further research into a number of disorders. Long-term alcohol use, for example, has shown changes in gene expression in the brain, and specific changes in cell types that may be associated with alcohol use disorders. These changes have been noted in synaptic transcripts in the prefrontal cortex, and are seen as factors that induce a drive for alcohol dependence, as well as misuse of other substances.
Other related studies also show evidence of synaptic changes and their loss, in the aging brain. Changes in gene expression alter protein levels in various pathways and this has been shown to be evident in synaptic or diseased contact dysfunction. This dysfunction has been seen to affect many brain structures and has a noticeable effect on the inhibitory neurons that lead to decreased levels of neurotransmission, and subsequent cognitive and disease declines.
Clinical interests
General
Brain damage or brain injury can manifest in many ways. Traumatic brain injuries, such as those received in contact sports, after a fall, or a traffic accident or work accident, can be attributed to immediate and long-term problems. Immediate problems may include bleeding in the brain, this can suppress the brain tissue or damage the blood supply. Bruises to the brain can occur. Bruising can cause extensive damage to the nerve tract that can cause diffuse axonal injury conditions. Cracked skulls, injuries to certain areas, deafness, and concussions can also occur soon. In addition to the location of the injury, the opposite side of the brain may be affected, called a contrecoup injury. Long-term problems that may develop include post-traumatic stress disorder, and hydrocephalus. Chronic traumatic encephalopathy may develop after multiple head injuries.
Neurodegenerative disease causes progressive damage to different parts of the brain function, and worsens with age. Common examples include dementia such as Alzheimer's disease, alcoholic dementia or vascular dementia; Parkinson's disease; and other more rare infections, genetic or metabolic causes such as Huntington's disease, motor neurone disease, HIV dementia, syphilis-related dementia and Wilson's disease. Neurodegenerative diseases can affect different parts of the brain, and can affect movement, memory, and cognition.
The brain, although protected by a blood-brain barrier, can be affected by infections including viruses, bacteria and fungi. Infection may be meninges (meningitis), brain problems (encephalitis), or in the brain (such as cerebral abscess). Rare prion diseases include Creutzfeldt-Jakob disease and its variants, and the kuru can also affect the brain.
Brain tumors can be benign or cancerous. The most malignant tumors come from other parts of the body, most commonly from the lungs, breast and skin. Brain tissue cancer can also occur, and comes from tissues in and around the brain. Meningioma, cancer meninges around the brain, more common than brain tissue cancer. Cancer in the brain can cause symptoms associated with their size or position, with symptoms including headache and nausea, or a gradual development of focal symptoms such as difficulty seeing, swallowing, speaking, or as mood swings gradually. Cancer is generally investigated through the use of CT scans and MRI scans. Various other tests including blood tests and lumbar puncture can be used to investigate the causes of cancer and evaluate the type and stage of cancer. Dexamethasone corticosteroids are often given to reduce the swelling of the brain tissue around the tumor. Surgery may be considered, but given the complex nature of many tumors or based on the stage or type of tumor, radiotherapy or chemotherapy may be considered more suitable.
Mental disorders, such as major depressive disorder, schizophrenia, bipolar disorder, post-traumatic stress disorder, attention deficit hyperactivity disorder, obsessive-compulsive disorder, Tourette syndrome, and addiction are known to be associated with brain function. Treatment for mental disorders may include psychotherapy, psychiatry, social intervention and personal recovery work or cognitive behavioral therapy; the underlying problems and associated prognosis vary significantly between individuals.
Epileptic seizures are thought to be associated with abnormal electrical activity. Seizure activity may manifest as an absence (awareness), focal effects such as leg movement or speech impediment, or generalized in nature. The status of epilepticus refers to a seizure or a series of seizures that have not expired in 30 minutes, although this definition has recently been revised. Seizures have many causes, but many seizures occur without the definitive cause found. In someone with epilepsy, risk factors for further seizures may include sleep deprivation, drug and alcohol intake, and stress. Seizures can be assessed using blood, EEG and various medical imaging techniques based on medical history and exam findings. In addition to treating underlying causes and reducing exposure to risk factors, anticonvulsant drugs may play a role in preventing further seizures.
Some brain disorders such as Tay-Sachs disease are congenital, and are associated with genetic mutations and chromosomes. A rare congenital cephalic disorder known as lissencephaly is characterized by a lack, or inadequate, cortical fold. The normal development of the brain can be affected during pregnancy by nutritional deficiencies, teratogens, infectious diseases, and with the use of drugs and alcohol.
Stroke
A stroke is a decrease in blood supply to the area of ​​the brain that causes cell death and brain injury. This can cause a variety of symptoms, including the "FAST" symptoms of drooping faces, arm weakness, and speech impediment (including by speaking and finding words or forming sentences). Symptoms relate to the function of the affected area of ​​the brain and may lead to the site and cause of stroke. Difficulties with movement, speech, or vision are usually associated with the cerebrum, whereas imbalances, double vision, vertigo and symptoms affecting more than one side of the body are usually associated with the brain stem or cerebellum.
Most strokes are caused by loss of blood supply, usually due to embolus, rupture of fatty plaque or small artery narrowing. Stroke can also occur due to bleeding in the brain. Transient ischemic attacks (TIAs) are strokes where symptoms improve within 24 hours. Investigation of a stroke will involve medical examination (including neurological examination) and the taking of a medical history, focusing on the duration of symptoms and risk factors (including high blood pressure, atrial fibrillation, and smoking). Further investigation is needed in younger patients. EKG and biotelemetry can be performed to identify atrial fibrillation; Ultrasound can investigate the narrowing of the carotid arteries; echocardiogram may be used to look for clots in the heart, valvular heart disease or the presence of a patent foramen ovale. Blood tests are routinely performed as part of the examination including diabetes tests and lipid profiles.
Some treatments for stroke are very important. These include clot freezing or clot removal surgery for ischemic stroke, and decompression for hemorrhagic stroke. Because stroke is a critical time, hospitals and even stroke treatments in hospitals involve accelerated inquiry - usually a CT scan to investigate haemorrhagic stroke and CT or MR angiogram to evaluate the arteries supplying the brain. MRI scans, not widely available, may indicate areas of the affected brain more accurately, especially with ischemic stroke.
After a stroke, a person can be treated in a stroke unit, and treatment can be directed as a future stroke prevention, including ongoing anticoagulants (such as aspirin or clopidogrel), antihypertensives, and lipid-lowering drugs. Multidisciplinary teams including speech pathologists, physiotherapists, occupational therapists, and psychologists play a major role in supporting a person who is affected by their stroke and rehabilitation.
Brain death
Brain death refers to a total loss of unchangeable brain function. It is characterized by coma, loss of reflexes, and apnea; however, brain death statements vary geographically and are not always accepted. In some countries there is also a syndrome that defined brain stem death. Declaration of brain death can have profound implications because declarations, under the principle of medical futility, will be attributed to the withdrawal of life support, and as people with brain death often have organs suitable for organ donors. This process is often made more difficult by poor communication with the patient's family.
When brain death is suspected, reversible reversible diagnoses such as hypothermia coma triggered, electrolytes, neurologic and drug-related cognitive suppression need to be excluded. Reflex testing can help in decisions, such as lack of response and breathing. Clinical observations, including lack of response, known diagnoses, and neural imaging, may all play a role in the decision to express brain death.
Society and culture
Neuroanthropology is the study of the relationship between culture and the brain. It explores how the brain evokes culture, and how culture affects brain development. Cultural differences and their relationship to brain development and structure are examined in various fields.
Mind
The philosophy of mind studies issues such as the problem of awareness and mind-body problems. The relationship between brain and mind is a significant challenge both philosophically and scientifically. This is because of the difficulty in explaining how mental activity, such as thoughts and emotions, can be implemented by physical structures such as neurons and synapses, or by other types of physical mechanisms. This difficulty is expressed by Gottfried Leibniz in the analogy known as Leibniz's Mill :
One must recognize that perception and what depends on it can not be explained on mechanical principles, that is, by numbers and movements. In imagining that there is a machine whose construction will allow it to think, to perceive, and to have perception, one can imagine it enlarging while maintaining the same proportions, so that one can enter into it, as to the windmill. For example, one must, when visiting in it, find only the parts that encourage each other, and never anything that explains perception.
- - Leibniz, Monadology
Doubts about the possibility of mechanistic explanation of thought prompted Renà © ¨ Descartes, and most other philosophers with him, to dualism: the belief that the mind is to some degree detached from the brain. However, there is always a strong argument in the opposite direction. There is clear empirical evidence that physical manipulation, or injury to, the brain (eg with drugs or lesions, respectively) can affect the mind in a strong and intimate way. In the 19th century, the case of Phineas Gage, a railroad worker who was injured by a powerful iron rod passing through his brain, convinced both researchers and the public that cognitive functionality was localized in the brain. Following this line of thought, a large amount of empirical evidence for the close connection between brain activity and mental activity has led most contemporary neuroscientists and philosophers to be materialists, believing that mental phenomena are ultimately the result of, or can be reduced to, physical phenomena.
Brain size
Brain size and intelligence are not strongly related. Studies tend to show a small to moderate correlation (mean about 0.3 to 0.4) between brain volume and IQ. The most consistent relationship is observed in the frontal, temporal, and parietal, hippocampic, and cerebellum lobes, but this only takes into account the relatively small number of IQ variants, which have only partial relation to general and apparent intelligence. world performance.
Other animals, including whales and elephants, have larger brains than humans. However, when the ratio of brain-to-body mass is taken into account, the human brain is almost twice as big as the bottlenose dolphins, and three times larger than the chimpanzees. However, a high ratio does not necessarily indicate intelligence: very small animals have high ratios and treeshrew has the greatest intelligence of mammals.
In popular culture
Research has denied some common misconceptions about the brain. These include ancient and modern myths. It is not true that neurons are not replaced after the age of two; or only ten percent of the brain is used. Popular culture also overly simplifies lateralization of the brain, indicating that the function is really specific to one side of the brain or the other. Akio Mori sparked the term game of the brain for an unsupported theory that spending a long time playing video games harms the area of ​​the forebrain and expression of emotion and creativity.
Historically, the brain is featured in popular culture through phrenology, a pseudoscience that assigns personality attributes to different regions of the cortex. The cortex remains important in popular culture as discussed in books and satires. The brain features in science fiction, with themes such as brain transplants and cyborgs (creatures with partial brain-like features). The 1942 science fiction book (adapted three times for the movie) Donovan's Brain tells the story of an in vitro isolated live brain, which is gradually taken over by evil intelligence.
History
Initial history
The Edwin Smith Papyrus, an ancient Egyptian medical treatise written in the 17th century BC, contains the earliest recorded reference to the brain. Hieroglyphs for the brain, occurring eight times in this papyrus, describe the symptoms, diagnosis, and prognosis of two traumatic injuries to the head. The papyri mentions the external surface of the brain, the effects of injury (including seizures and aphasia), meninges, and cerebrospinal fluid.
In the fifth century BC, Alcmaeon of Croton at Magna Grecia, first considered the brain as the seat of the mind. Also in the 5th century BC in Athens, Hippocrates believed that the brain was the center of intelligence. Aristotle, in his biology originally believed that the heart was the center of intelligence, and saw the brain as a cooling mechanism for blood. He reasoned that humans are more rational than animals because, among other reasons, they have a bigger brain to cool their hot blood. Aristotle describes meninges and distinguishes between cerebrum and cerebellum. Herophilus of Chalcedon in the fourth and third centuries BC distinguishes cerebrum and cerebellum, and provides the first clear picture of the ventricles; and with Erasistratus of Ceos experimenting on a living brain. Their works are now largely lost, and we know about their achievements largely due to secondary sources. Some of their discoveries must be rediscovered a millennium after their death. Doctor Anatomy Galen in the 2nd century, during the Roman Empire, dissected the brain of sheep, monkeys, dogs, and pigs. He concluded that, since the cerebellum is denser than the brain, the brain has to control the muscles, while the cerebrum is soft, it must be where the senses are processed. Galen further theorized that the brain functions with the movement of animal spirits through the ventricles.
Renaissance
In 1316, Mondino de Luzzi's
Source of the article : Wikipedia
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